feat: Implement Phase 2 dashboard for K8s agent system

Lightweight Go-based dashboard for Raspberry Pi cluster:

Backend:
- chi router with REST API
- Embedded static file serving
- JSON file-based state storage
- Health checks and CORS support

Frontend:
- Responsive dark theme UI
- Status view with nodes, alerts, ArgoCD apps
- Pending actions with approve/reject
- Action history and audit trail
- Workflow listing and manual triggers

Deployment:
- Multi-stage Dockerfile (small Alpine image)
- Kubernetes manifests with Pi 3 tolerations
- Resource limits: 32-64Mi memory, 10-100m CPU
- ArgoCD application manifest
- Kustomize configuration

API endpoints:
- GET /api/status - Cluster status
- GET/POST /api/pending - Action management
- GET /api/history - Action audit trail
- GET/POST /api/workflows - Workflow management

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dashboard/internal/models/models.go

@@ -0,0 +1,80 @@
+package models
+
+import "time"
+
+// ClusterStatus represents the overall cluster health
+type ClusterStatus struct {
+	Health    string       `json:"health"` // Healthy, Degraded, Critical
+	UpdatedAt time.Time    `json:"updated_at"`
+	Nodes     []NodeStatus `json:"nodes"`
+	Alerts    []Alert      `json:"alerts"`
+	Apps      []AppStatus  `json:"apps"`
+}
+
+// NodeStatus represents a single node's status
+type NodeStatus struct {
+	Name       string  `json:"name"`
+	Status     string  `json:"status"` // Ready, NotReady
+	CPU        float64 `json:"cpu_percent"`
+	Memory     float64 `json:"memory_percent"`
+	Conditions string  `json:"conditions"` // OK, MemoryPressure, DiskPressure, etc.
+}
+
+// Alert represents a Prometheus/Alertmanager alert
+type Alert struct {
+	Name        string    `json:"name"`
+	Severity    string    `json:"severity"` // warning, critical
+	Description string    `json:"description"`
+	FiringAt    time.Time `json:"firing_at"`
+}
+
+// AppStatus represents an ArgoCD application status
+type AppStatus struct {
+	Name       string `json:"name"`
+	SyncStatus string `json:"sync_status"` // Synced, OutOfSync
+	Health     string `json:"health"`      // Healthy, Progressing, Degraded
+	Revision   string `json:"revision"`
+}
+
+// PendingAction represents an action awaiting user approval
+type PendingAction struct {
+	ID          string                 `json:"id"`
+	CreatedAt   time.Time              `json:"created_at"`
+	Agent       string                 `json:"agent"`
+	Action      string                 `json:"action"`
+	Description string                 `json:"description"`
+	Details     map[string]interface{} `json:"details"`
+	Risk        string                 `json:"risk"` // low, medium, high
+	Workflow    string                 `json:"workflow,omitempty"`
+}
+
+// ActionDecision represents the user's decision on a pending action
+type ActionDecision struct {
+	ID         string    `json:"id"`
+	Decision   string    `json:"decision"` // approved, rejected
+	DecidedAt  time.Time `json:"decided_at"`
+	DecidedBy  string    `json:"decided_by,omitempty"`
+	Reason     string    `json:"reason,omitempty"`
+}
+
+// ActionHistory represents a completed action
+type ActionHistory struct {
+	ID          string                 `json:"id"`
+	Timestamp   time.Time              `json:"timestamp"`
+	Agent       string                 `json:"agent"`
+	Action      string                 `json:"action"`
+	Description string                 `json:"description"`
+	Details     map[string]interface{} `json:"details,omitempty"`
+	Result      string                 `json:"result"` // success, failed
+	AutoApproved bool                  `json:"auto_approved"`
+	Workflow    string                 `json:"workflow,omitempty"`
+}
+
+// Workflow represents a defined workflow
+type Workflow struct {
+	Name        string   `json:"name"`
+	Description string   `json:"description"`
+	Triggers    []string `json:"triggers"`
+	LastRun     *time.Time `json:"last_run,omitempty"`
+	Status      string   `json:"status,omitempty"` // idle, running, completed, failed
+}